[Emailcore] MDAs (was: Re: Delivered-To issues)

[John C Klensin <[e-mail]>]

(note subject line change and see "p.s." at end)

--On Thursday, January 7, 2021 10:16 +0100 Alessandro Vesely
<[e-mail]> wrote:

> On Wed 06/Jan/2021 18:07:17 +0100 John Levine wrote:
>> In article <[e-mail]> you
>> write:
>>> This discussion brought up another defect of RFC 5321,
>>> methinks.  It does not  define a straight line between an
>>> MTA and an MDA. ...
>> 
>> I think the problem is worse than that. What we're calling an
>> MDA combines two separate things.  RFC 5598 calls them the
>> hMDA and rMDA.
>> 
>> The hMDA is more or less the thing that takes an incoming
>> message and disposes of it, by storing it in a file or
>> otherwise. Most MTAs have a few simple default hMDA and ways
>> to call out to more complex ones like procmail, maildrop, and
>> Sieve.
>> 
>> I don't see any point in trying to rewrite 5321 to try to
>> separate out an hMDA that might be in the MTA and might not.
> 
> 
> Some points can be made without splitting hairs.  Defining the
> concept of MDA only serves to clearly state what is part of
> SMTP and what is beyond.

But, AFAICT, that brings things full circle to John L's point.
If there are some flavors of MDA that are really part of the MTA
function and some flavors that are not, then a crisp definition
of MDA that would fit well into 5321bis may not be possible
without splitting exactly those hairs.

I'd be happy to be wrong about this.  However, the only way I
can think of to would figure what can practically be done within
the text of 5321bis and constraints on it would be to see
proposed text, one that, as needed, references other standards
track documents for definitions.   I await such text.

best,
    john

p.s. I have changed the subject line because this is really
about MDAs, their definition, and their relationship to 5321bis.
Certainly it would be desirable for a description of
Delivered-To: (or Envelope-To:) in some other spec to reference
such text if it appeared in 5321bis but, as I suggested in a
note posted a few minutes ago, I believe that those (or other)
new headers are out of scope for 5321bis and the WG and do not
intend to spend more time reading that thread unless the WG
Co-chairs direct otherwise.

> 
> 
> Best
> Ale
> --